We propose to continue studies of the ultrastructure of the two distinct auditory end-organs in macaques, the inner and outer hair cell systems. Further elucidation of their differences in connectivity, and especially of their possible interaction in the organ of Corti, will be attempted. The functional significance of the double hair cell system of the organ of Corti in mammals is a key problem of auditory physiology, but as yet there is no real understanding. In addition to analysis of normal monkeys, we propose to selectively denervate the crossed and uncrossed components of the nerve fiber system which passes outward from the brain stem to make synaptic contact with hair cells and with the afferent dendrites. This will be done surgically rather than through the more or less selective destruction of outer hair cells with antibiotics such as di-hydro-streptomycin. It is hoped to determine whether the out-going nerve fibers are comprised of a single system or separate pathways to inner and outer hair cells respectively.